DESCRIPTION (From the Applicant?s Abstract): The overall, long-term objective of this research is to gain an understanding of the mechanisms and pathways that influence signaling in photoreceptors. Regulators of visual transduction are incompletely understood at present. Characterizing the regulatory proteins that modulate phototransduction is essential in understanding both retinal physiology and pathology. The research proposed will examine the influence of a potentially important modulator of G-protein signaling, caveolin, in photoreceptor outer segments. The goals of this application are to demonstrate whether caveolin is a bon fide outer segment protein, to determine whether caveolin associates with the photoreceptor G-protein, transducin, to determine whether this association influences transducin activity, and to examine, in vivo, potential light/dark-mediated effects on caveolin/transducing association. The presence of caveolin in outer segments will be assessed by careful cell fractionation, immunoblot analysis ad immunocytochemistry. Caveolin/transducin interactions will be determined by immunoprecipitation and direct protein-protein binding experiments with purified transducin and expressed caveolin fusion protein. In addition, the effect of caveolin-derived peptides on nucleotide exchange and GTPase ctivity of transducin alpha subunits will be assessed.